Effects of pH, extrusion tip size and storage protocol on the structural properties of Ca(II)-alginate beads.

The Ca(II)-alginate beads were formulated changing some synthesis variables: pH (3.8-6.8), extrusion tip size (0.25-0.50 mm) and washing/storage protocol, to evaluate possible implications in the structural properties of beads, which are critical to scale and standardize their production at industrial level. Regardless of the macro- (diameter, area, perimeter and roundness, studied by image analysis) and micro-structural (size, density and interconnectivity of rods assessed by SAXS) parameters analyzed, there are no effects related to the washing and storage protocol employed for any synthesis conditions. Structural parameters are only influenced by the synthesis pH. Both washing protocol and extrusion tip size effects on the consolidation of the alginate network are negligible at each pH value. Besides, none of the synthesis variables affected the availability of water within the beads as assessed by diffusion coefficient and water activity measurements. A model, relating chain-chain interactions and polymer chain packing, is proposed.